Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$72.48	10.622%	$80.1788	$80.18	$80.20	$80.20
Purchase #2	$64.72	12.564%	$72.8514	$72.85	$72.85	$72.90
Purchase #3	$235.36	4.304%	$245.4899	$245.49	$245.50	$245.50
Purchase #4	$51.37	7.301%	$55.1205	$55.12	$55.10	$55.10
Purchase #5	$203.52	12.151%	$228.2497	$228.25	$228.25	$228.20
Purchase #6	$204.79	3.693%	$212.3529	$212.35	$212.35	$212.40
Purchase #7	$99.79	3.399%	$103.1819	$103.18	$103.20	$103.20
7 purchase totals =	$932.03		$997.4251	$997.42	$997.45	$997.50